The present invention relates to stripping optical fibers and in particular to a device for stripping optical fiber ribbons.
Optical fibers are presently widely used for communicating information such as in large telecommunication systems, primarily owing to their large reliability, their insensitivity to electrical interference and their high capacity. In order to facilitate handling optical fibers, they are often provided as fiber ribbons, in which a plurality of optical fibres are located adjacent to each other, optically isolated from each other and from the environment, but in some manner fixed in parallel to each other, for example by means of a polymer coating. Such a ribbon usually contains 4, 6, 8 or 12 parallel fibers.
When splicing two different fibers, which is usually performed by welding, the polymer coatings of the fibers must first be removed. Thus, both the individual coating of the fibers and the material, which secures the fibers to each other to form a fiber ribbon, must be removed. Thereupon the uncovered fibres are cut in order to thereafter be welded together.
In order to strip the coatings, the entire fiber ribbon is first heated, see for example the fiber tool disclosed in Swedish patent application 9103492-6. This heating softens the coatings resulting in a reduction of friction forces which are to be overcome when stripping the fibers. Thereafter the primary coating is removed by means of two blades having opposite edges, which pinch the fiber ribbon at a location about 35-50 mm from an end thereof. Then a tensional force is applied to the end of the fiber ribbon, which results in mainly two possible outcomes:
1. The coating is pulled away in the shape of a complete polymer part or sleeve.
2. The coating is scraped away forming small particles which can adhere to various objects such as the stripped fiber ends.
The first of these two cases is of course desirable. If the fiber ribbon when being heated is made too soft, i.e. the fiber ribbon end is subjected to a too high temperature during a too long time period, the fiber ribbon is easily deformed and then the very elastic coating is torn to pieces, which also is undesirable. Thus, in order to perform a satisfactory stripping operation, the ribbon fiber end should be subjected to an adequate temperature during a suitable time period. Usually, the temperature and the time period are set by making a plurality of stripping tests for each new type of fiber ribbon, which is to stripped and spliced. It even turns out that for many fiber types it is very difficult for find suitable stripping parameters and in any case a lot of testing work is required. This is of course time consuming and thus some method would be searched for in order to reduce the effort in setting the correct parameter values.
It is an object of the invention to provide a method and device for stripping an optical fiber which can in a reliable and reproducible way remove coatings from in particular optical fiber ribbons without making any extensive testing of the adhesion of the coating.
Generally an optical fiber and in particular a fiber ribbon is stripped from a polymer coating by first determining a first end portion of the fiber to be rid of the coating. Then the fiber is clamped at a second portion adjacent the first portion in a cutting and tension unit. In the clamping operation knifes are pressed into the polymer coating at a position between the first and second regions. Thereupon the first portion is clamped and heated in a heating unit. Finally the cutting and tension unit is moved away from the heating device and then the knifes separate the coating on the first portion from the rest of fiber. An empty polymer sleeve is left in the heating device. When starting to move the cutting and tension unit it is not affected by any manual force but only by an elastic predetermined force derived from a spring. The predetermined force has a direction so that it acts to separate the heating unit and cutting and tension unit from each other. After the start of the movement, the movement is fulfilled by manually pulling the two units apart.
Linear guide means are arranged to guide the units in movements towards and away from each other. The spring is provided as an elastic means which thus acts to move the units away from each other and preferably acts on a first one of the units. The elastic means is thus only active to start the movement of the units from each other and only up to a position, in which there is a rather small, predetermined distance between the units. The elastic means acts freely meaning that it allows that the units are separated from each other by more than the first distance, not making any obstacle to this movement, when there is no elastic action. The elastic means can comprise an elastically biased rod in one of the units and then this rod acts with an end surface freely on a surface of the first unit. The guide means can then comprise cylindrical guide rods which are attached to and extend from one of the units into corresponding bores made in the other one of the units and which are parallel to the spring-loaded rod.